Append a Header for CSV file?

Question

I am trying to add a header to my CSV file.

I am importing data from a .csv file which has two columns of data, each containing float numbers. Example:

  11   22
  33   44
  55   66

Now I want to add a header for both columns like:

 ColA  ColB
  11    22
  33    44
  55    66

I have tried this:

with open('mycsvfile.csv', 'a') as f:
    writer = csv.writer(f)
    writer.writerow(('ColA', 'ColB'))

I used 'a' to append the data, but this added the values in the bottom row of the file instead of the first row. Is there any way I can fix it?

Answer 1

One way is to read all the data in, then overwrite the file with the header and write the data out again. This might not be practical with a large CSV file:

#!python3
import csv
with open('file.csv',newline='') as f:
    r = csv.reader(f)
    data = [line for line in r]
with open('file.csv','w',newline='') as f:
    w = csv.writer(f)
    w.writerow(['ColA','ColB'])
    w.writerows(data)

Answer 2

i think you should use pandas to read the csv file, insert the column headers/labels, and emit out the new csv file. assuming your csv file is comma-delimited. something like this should work:

   from pandas import read_csv

   df = read_csv('test.csv')
   df.columns = ['a', 'b']
   df.to_csv('test_2.csv')